To get started you add a single autoload form to your .emacs file and
then issue the corresponding M-x command. The file
emacs/emacs-acl2.el under the ACL2 distribution contains everything
you need to get started, and more. Alternatively put the following
into your .emacs file, first replacing `v2-x' in order to point
to the current ACL2 release.

Once the above is taken care of, then to start using proof trees you
do two things. In emacs, evaluate:

M-x start-proof-tree

Also, in your ACL2, evaluate

:start-proof-tree

If you want to turn off proof trees, evaluate this in emacs

M-x stop-proof-tree

and evaluate this in your ACL2 session:

:stop-proof-tree

When you do meta-x start-proof-tree for the first time in your emacs
session, you will be prompted for some information. You can avoid the
prompt by putting the following in your .emacs file. The defaults are
as shown, but you can of course change them.

The file interface/emacs/README.doc discusses an extension of ACL2
proof trees that allows the mouse to be used with menus. That
extension may well work, but it is no longer supported. The basic
proof tree interface, however, is supported and is what is described
in detail elsewhere; see proof-tree. Thanks to Mike Smith for
his major role in providing emacs support for proof trees.